Problem: Kevin ate 1 slice of pizza. Tiffany ate 1 slice. If Kevin ate $\dfrac{1}{5}$ of the pizza, what fraction of the pizza was eaten?
Explanation: If 1 slice represents $\dfrac{1}{5}$ of the pizza, there must have been a total of 5 slices. $\text{fraction of pizza eaten} = \dfrac{\text{number of slices eaten}}{\text{number of slices total}}$ They ate ${2}$ out of $5$ slices. They ate $\dfrac{2}{5}$ of the pizza.